Pronounced fringing, particularly in high contrast areas. Lens cap needs to be replaced right out of the box - a broken-record complaint for Zeiss' entire lens lineup.

A beautifully built, terrifically sharp macro lens. There is also that 3-D depth perception that I just don't feel is present in the Canon 100 macros.

I have owned both of the Canon 100mm macro lenses, and was thrilled with each of them. They are both very sharp, but don't possess the same "oomph" as the Zeiss. The Zeiss' 3D look is, I think, what separates it.

The best way I can think to describe the difference is that with the Canons you are looking through a window, and with the Zeiss, you've opened the window and are just looking at the scene. (Granted, it is a very clean window).

However, there is a pronounced issue with colour fringing when photographing high contrast scenes. This is certainly much more pronounced than in the Canon alternatives. If you take a picture of a leaf-less tree against a white winter sky, the tree will have a distinct purple glow to it.

The fringing is is not a fatal flaw, but you need to be aware of it. Sometimes, slight adjustment to how you photograph something can completely eliminate the problem. Other times, you'll need to do some adjustment in post.

The lens does do an outstanding job, and I was happy to trade my most recent Canon to get it.

Other differences are, obviously, that it does not have autofocus, and as compared to the 100L or most recent Nikon, does not have image stabilisation/vibration reduction. I did find that stabilisation was particularly nice for tripod-free wandering around macro work, and I do miss this. The lens also "only" focuses down to a 1:2 reproduction ratio, which I have not really found to be especially noticeable... but obviously, this will vary with your desired subject matter. (The lens is, obviously, compatible with extension tubes, though).

One annoyance for macro work, though, is that the chrome end of the barrel is easily reflected against reflective subject matter. A filter solves this, but without this it seems like a silly oversight for a macro lens.

The lens also scores over the Nikon and Canon macro offerings with an f/2 maximum aperture, and is still very sharp wide open.

As a walkaround lens, too, focused at infinity, the Zeiss is significantly shorter than either the Canon or Nikon offerings, and turns fewer heads on the street.

I have next to no experience with the Canon 100mm f/2, or the Nikon 105DC, and so can't comment on how the Zeiss compares to either of these non-macro, portrait-oriented lenses. I will say, though, the one time I handled the canon 100/2, I found the minimum focusing distance to be prohibitively large for what I would term "general purpose detail shots" - like a person's hand writing a note, or a tight-ish crop on a person's head.

I certainly find the bokeh on the Zeiss to be wonderfully smooth, as well. I have not used the venerable Nikon 105/2.5 enough, nor used the ZE100 enough for portraiture to really be able to compare these two, but my impression is that this would be a close race.

Very high sharpness (in my copy, straight to the corners, unlike some other reviewers), rich colours, and a surprisingly strong 3D effect wide open (especially given that this is both a wide angle lens, and "merely" f/2.8)

Cons:

Some distortion in the corners, apparently. Lens cap needs to be replaced right out of the box - a broken-record complaint for Zeiss' entire lens lineup.

This is the nicest wide angle lens that I have used!

A very close second is the Leica 24mm Elmarit-M ASPH. The Zeiss matches the Leica's incredible sharpness and contrast, and the wide angle images just beg to be scrutinised and perused for every last tiny morsel of detail.

I have also used the Nikon AF-S 17-35, Canon 17-40, and Canon 16-35II. I find the Zeiss easily supplants the Canon offerings, especially when looking off-centre. I found that the images from the Zeiss were just more compelling in terms of sharpness and contrast than those from the highly-regarded 17-35, but not by a huge margin.

Another similar lens that I still own and currently use is the Canon 24Lmk2. The Zeiss' contrast and sharpness, again, just feel a little bit higher and compelling, and the out-of-focus areas are a bit smoother. The 24/1.4 a very good lens, but the Zeiss, again, just possesses a certain added quality.

Above all, though, shockingly, I find the Zeiss 21mm is able to exhibit that 3D look that so many other lenses in the lineup are fabled for, despite being a wide angle lens with 2.8 maximum aperture. The effect isn't as pronounced as it is with higher focal lengths, but is still very present. The quality of the out-of-focus areas, in tandem with the terrific sharpness would seem to play a large roll in this. It is in this regard that the lens really wins out over all of the other wide angle lenses that i have mentioned.

The ZE21 seems to me even to echo my old Hasselblad CF 50mm FLE in its 3D rendering.

The Canon 24LmkII is able to do a good job at creating depth with its 1.4 aperture, but the Zeiss still wins out, to my eye, in making it seem real. The Canon 24/1.4 is able to emphasize the focal plane apart from the fore- and backgrounds, but the Zeiss still makes me feel more as though I am looking at a real scene. It isn't a matter of the one feeling more or less out-of-focus, it is a matter of the sense that if I move my head to the side a bit, more of the background will reveal itself behind the subject.

Architectural photographers will notice some funny distortion in the corners. In street and landscape photography, I have never, ever noticed this. I gather that Adobe lens profiles for the lens solve the issue satisfactorily.

For landscape work, the Zeiss 21mm handles being stopped down to f/16 very well.

The front of the lens, which takes an 82mm, is a little wide, and even moreso with the hood. I find I have to be a bit more organised with packing my shoulder bag, as the bulk does affect the ease with which the lens can be quickly stowed or grabbed. I find the weight to be quite nice and appropriate. The focus is very smooth, and the narrower barrel around the focusing ring is especially comfortable and quick to adjust.

All in all, if you are in search of a wide angle prime lens, I would recommend this lens without reservation, so long as you are not in need of autofocus.

It is, again, the very nicest wide angle lens that I feel I have ever had the pleasure of using!

Lens cap needs to be replaced right out of the box - a broken-record complaint for Zeiss' entire lens lineup.

This is a truly stunning lens.

I also have the Canon 135/2L, which I have always thought was a wonderfully sharp lens. The Zeiss, without hesitation, trumps it in terms of sharpness. Even at f/2 the Zeiss challenges the Canon lens stopped-down.

The ZE 135 also has a very smooth bokeh, and the focus transition (going into and then out-of focus) is very subtle and realistic.

The quality of the bokeh, especially when contrasted with the wonderfully crisp in-focus sharpness, and then the handing of the focus transition, lend the Zeiss that wonderfully compelling 3-D look to its images.

The 135mm focal length has its uses, and they are obviously not universal. If you like the focal length, and aren't in so much of a hurry as to need autofocus, this lens is truly sensational and I feel worth the hefty price tag.